For example, from the document DE 42 30 534 A1 a drive unit for a vehicle steered by speed difference is known, with running gear mechanisms that roll on a supporting surface, in particular caterpillar or track mechanisms. The vehicle comprises a drive engine which powers a branching or connecting transmission, this in turn driving a gearshift transmission and the two auxiliary drives. The two guide rollers of the caterpillar or track mechanisms are driven by the transmission output of the gearshift transmission. In addition, associated with each track mechanism there is a summation gear system as a steering gear. In the known drive unit the drive engine with the transmission components, which consist of the branching transmission for branching the drive input for the auxiliary transmissions, the gearshift transmission, the output of the main transmission and the summation gears, are all combined in one block. Thus, a so-termed power-pack is formed, which consists of the engine, the transmission and the steering gear. The concentrated mass density of the power-pack disadvantageously displaces the center of gravity of the vehicle when it is fitted at the rear or at the front of the vehicle. Furthermore, a power-pack fitted at the rear impedes access of the vehicle's crew from the rear. If the power-pack is fitted at the front of the vehicle, the final drive of the tracks is usually also at the front and therefore has an adverse effect on the loading of the tracks and on the track wear.